Maiduguri, Nigeria - Nigeria's government says negotiations with Boko Haram continue for the release of the remaining Chibok schoolgirls who were kidnapped three years ago by the extremist group, shocking the world.

The government "has gone quite far with negotiations," Vice President Yemi Osinbajo said Wednesday night.

He spoke shortly before Friday's three-year anniversary of the mass abduction of 276 schoolgirls from a village in the country's northeast. At least 195 of them remain captive.

Nigeria in October announced the release of 21 Chibok schoolgirls, saying for the first time that it had been negotiating with the extremist group, mediated by the Swiss government and the International Committee of the Red Cross. The government denied a ransom was paid and that it had freed some detained Boko Haram fighters in exchange for the girls.

At the time, officials said they were pressing on with negotiations and expected the release of a second group of 83 girls "very soon." No more have been freed.

Osinbajo indicated that Nigeria has faced some challenges in the latest negotiations but didn't give details, citing security reasons.

The failure of Nigeria's former government to act quickly to free the girls sparked a global Bring Back Our Girls movement. Members of the movement demonstrated on Thursday in Lagos, Nigeria's commercial hub, demanding that the government do more.

The vice president said securing the safe release of the schoolgirls and others held by Boko Haram is "a matter of conscience."

Nigeria's military in the past year has rescued thousands of Boko Haram captives while liberating towns and villages from the group's control, but many have been detained as possible Boko Haram suspects.

The Nigeria-based Boko Haram's seven-year Islamic uprising has killed more than 20,000 people and driven 2.6 million from their homes, with millions facing starvation.